Protective device for liquid immersed electrical apparatus



Aug. 15, 1939. E. D. TREANOR 2,169,857

PROTECTIVE DEVICE FOR LIQUID IMMERSED ELECTRICAL APPARATUS Filed July 50, 1958 WWW xm i" Zz/20 ,2/ bbl Hi Attorney.

Patented Aug. 15, 1939 PATENT OFFICE PROTECTIVE DEVICE FOR LIQUID IMQ- MERSED ELECTRICAL APPARATUS Edward D. Treanor, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application July 30, 1938, Serial N0. 222,203

4 Claims.

My invention relates to protective devices for liquid-immersed electrical apparatus such as transformers and reactors. In accordance with the invention the transformer o1' other electrical 5 apparatus is immersed in an insulating liquid within a sealed casing which is only partially iilled with the liquid so that there is a space iilled with air or other gas above the surface of the liquid. Changes in the temperature of the liquid due to different load and ambient temperature conditions cause the liquid to expand and contract with corresponding slow changes in the pressure of the gas above the liquid. Trouble in the apparatus, such as the breakdown of insulation and an arc, however, will cause evolution of additional gas and a rapid increase in pressure within the space of the liquid.

The general object of the invention is to provide an improved protective device for transformers or other electrical apparatus which will respond to a rapid increase in pressure caused by trouble in the apparatus but will not respond to a slow increase in pressure due to changes in normal operating conditions. The protective device may include any form of protective circuit, such as a signal for calling the attention of an attendant to the fact that there is trouble in the apparatus so that he may take proper steps to prevent further trouble, or such as an automatic 30 circuit for disconnecting the apparatus.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1 shows a liquid-immersed transformer provided with a protective device constructed in accordance with the invention, a portion of the transformer casing being broken away to show the transformer and its protective device; Fig. 2 is an enlarged sectional View of the protective device; and Fig. 3 indicates a protective circuit different from that shown in Fig. l.

Like reference characters indicate similar parts inthe different figures of the drawing.

The transformer IB, shown in Fig. l, is immersed in a body of insulating liquid II within a sealed casing I 2, the liquid I partially lling the casing I2 to leave a space for air or other gas I3 above the surface of the liquid. Changes in the temperature of the liquid II, due to changes in load and ambient temperature conditions, will cause corresponding changes in the temperature,

volume and pressure of the gas I3. Such changes are, however, comparatively slow. Trouble in the transformer, such as a breakdown of insulation i5 accompanied by an arc, however, will cause a (Cl. 20G-81) rapid evolution of gas and a consequent rapid increase in pressure within the casing I2. t is obviously desirable that any protective device respond to the rapid increase in pressure resulting from trouble in the apparatus but that no response occur to the slow increase in pressure resulting from normal temperature and pressure changes due to changes in load and ambient temperature conditions.

'Ihe protective device I4, as shown most clearly in Fig. 2, includes a cork float I5 in the form of a hollow ring which floats on the surface of the liquid Il and supports a light metal vessel IE shaped somewhat like an inverted bottle with its open neck Il extending down into the liquid II through the opening I8 in the float I 5 and opening below the surface of the liquid. A second cork iioat I 9 floats on the surface of the liquid i I inside the neck Il of the vessel I6 and a movable Contact 20 is secured to this stem 2 I. A guide 22 keeps the float I 9 away from the sides of the neck Il of the vessel I3. A small hole 23 in the top of the vessel I6 permits a slow interchange of gas between the space 24 within the vessel I 6 and the space I3 outside of this vessel I6 and above the liquid il. The pressures in the spaces 24 and I3 are therefore always substantially the same so long as any change in the pressure of the gas in the space I3 above the liquid I I takes place slowly. If any trouble in the transformer ID causes the pressure of the gas I3 to increase rapidly, however, the pressure of the gas within the space 24 in the vessel I6 will increase more slowly because gas cannot pass rapidly through the restricted opening 23. This greater pressure of the gas in the space I3 outside the vessel I6 will force the liquid to rise inside the neck Il of the vessel and this will cause the small float I9 also to rise relatively to the vessel I G and its supporting float I5 so that the movable contact 20 will connect the two contacts 25 which are secured to the float I5 and the vessel I. These contacts control a protective circuit 25 which, as shown in Fig. 1, includes a battery 2'! with a bell 28 to call the attention of an attendant to the trouble in the transformer I so that he may disconnect the transformer or take other proper steps to avoid further damage. If desired, the protective circuit 2B may, as shown in Fig. 3, in-

clude a battery 2l and an automatic switch 23 for d disconnecting the transformer. 'Ihe device I4 may be retained in any desirable position on the surface of the liquid II by a link 3B pivoted at one end to the device I4 and at the other end to the side wall of the casing l2.

second float I9 by a L The invention provides a simple and reliable protective device for liquid-immersed transformers or other electrical apparatus and a device which will respond in case of electrical trouble in the apparatus, but which cannot give false responses to such slow temperature and pressure changes as occur during normal operation of the apparatus.

The invention has been explained in connection with a liquid-immersed transformer but changesV and other applications may obviously be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire tosecure by Letters Patent of the United States is,-

1. A protective device arranged to float on the surface of insulating liquid, said device including a hollow vessel having an opening at its lower end, a second float within said opening, a cont-act carried by the second float, and cooperating contacts secured to said vessel, said Vessel having a restricted opening in its upper portion.

2. A protective device for liquid-immersed electrical apparatus, said device including a float, a

hollow vessel carried by the iloat and having an opening at its lower end, a second float within said opening, a contact carried by the second float, and cooperating contacts secured to the first float and vessel, said vessel having a restricted opening in its upper portion.

3. A protective device for liquid-immersed electrical apparatus, said device including a ringshaped float, a hollow vessel carried by the float and extending through said oat with an opening below the surface of the liquid, a second oat within said opening, a Contact carried by the second float, and cooperating contacts secured to the first iloat and vessel, said vessel having a restricted opening above the surface of the liquid.

4. A protective device arranged to float on the surface of insulating liquid, said device including a hollow vessel having an opening at its lower end, a second float within said opening, and contacts carried by said floats for controlling a protective circuit, said vessel having a restricted opening in its upper portion.

EDWARD D. TREANOR. 

